Identification of Energy and Spatial Location of Electron Traps in AlGaN/GaN HFET Structures

We present a methodology, based on gated van der Pauw measurements, to identify the electron trap charging or discharging energy at different spatial locations in AlGaN/GaN heterostructures. The slow transient response of the 2-D electron gas concentration was recorded following different Schottky gate and substrate voltage pulses and at different temperatures. While recovering from a gate voltage stress, both trapping and detrapping processes are observed at different times and temperatures, demonstrating that dynamic rather than quasi-equilibrium considerations should be invoked to explain the data. Several distinct electron traps were identified, three traps located in the GaN buffer layer having detrapping activation energies of about 0.55, 0.45, and 0.21 eV, and an activation energy of about 0.64 eV was associated with trapping processes in the AlGaN barrier layer.